There are many possibilities! : The Travelcard, the Travelcard or Oyster Bus?
Travelcard
As a tourist, you can choose the Travelcard for 3 days or a week. This seems to be the best option. Especially if you use public transportation several times a day.
Price for 3 days in Zone 1-2: £ 18.40 or Zone 1-6: £ 9:20 p.m.
A Travelcard for the week can cost you £ 25.80 to £ 68.10 depending on the area where you want to travel. Ex: Zone 1-3: £ 30.20
To identify with Zones, please visit: www.tfl.gov.uk/gettingaround/1106.aspx
Oyster Oyster is a map that allows you to pay only a single trip time. You must pay your trips in advance by paying a credit of £ 5. The average price of a journey is £ 1.60 to £ 3.80.
Warning! Oyster does not work on the line Train: South West train service. £ 20 fine if you are caught with the wrong ticket transport.
* Reduced price for all cards for kids. Provide a photo ID.
Bus Travelcard
If you have a Travelcard Bus. This allows you to visit all of London, using the bus. That's really what is more economical, from the moment you have time.
Travelcard for the day pass £ 3.80, Bus Travelcard for the Week: £ 13.80.
You can find maps for the bus at the following site: http://www.tfl.gov.uk/gettingaround/9440.aspx